1. Field of the Invention
This invention relates generally to a thin film magnetic head used for recording and reproducing information in magnetic disk units, and more specifically to a thin film magnetic head comprising a lower magnetic core and an upper magnetic core disposed facing each other via a non-magnetic thin film serving as a magnetic gap, and a thin film coil wound on the magnetic core between the upper and lower magnetic cores, in which the length of a magnetic path formed through these magnetic cores can be reduced.
2. Description o the Related Art
A separate recording/reproduction type magnetic head comprises a magneto-resistive head and an inductive head laminated on a non-magnetic substrate 10 made of a material, such as alumina/titanium carbide, as shown in the perspective view of FIG. 10. The separate recording/reproduction magnetic head which is manufactured with thin film technology is often called a "thin film magnetic head" as a generic term. The inductive head has also heretofore been called the "thin film magnetic head". In this Specification, therefore, the term "thin film magnetic head" is used referring to the "separate recording/reproduction type magnetic head" and/or the "inductive head."
In FIG. 10, a thin film magnetic head has on a non-magnetic substrate 10 an alumina layer 12, a lower shield 13, a magneto-resistive element 14, a magnetic film 15 serving as an upper shield and a lower magnetic core (hereinafter referred to as "lower magnetic core"), and an upper magnetic core 16. In the figure, an insulating film for insulating between the layer shield, the magneto-resistive element and the upper shield is omitted. As shown in FIG. 11 illustrating the longitudinal section of the head shown in FIG. 10 in the gap depth direction, the head has a non-magnetic thin film 17 comprising alumina, etc. between the lower magnetic core 15 and the upper magnetic core 16. The non-magnetic thin film 17 serves as a magnetic gap, through which opposing ends of both magnetic films form magnetic poles 151 and 161 of the thin film magnetic head.
An exciting coil is wound between the lower magnetic core 15 and the upper magnetic core 16. A thin film coil is used as the exciting coil, with the number of turns of this coil being normally 10 to 15 turns to maintain the magnetic and electric conversion characteristics between the upper and lower magnetic cores and the coil. In order to reduce the inductance of the head by reducing the space occupied by the coil between the upper and lower magnetic cores, it has been commonly practiced to dispose the thin film coil in multiple, normally two, layers. A non-magnetic insulating resin layer is packed between the thin film conductors to insulate between the thin film conductors of the coil, and between the thin film conductors of the coil and the magnetic cores. FIG. 11 is a cross-sectional view of one head having a thin film coil arranged in two layers. As shown in the figure, an insulating resin layer 43 is formed on a non-magnetic thin film 17 deposited on a lower magnetic core 15. Since the non-magnetic thin film 17, made of alumina, etc., serves as a magnetic gap for the thin film magnetic head between both magnetic cores, the thickness thereof is as thin as 0.3 to 0.4 .mu.m, about the length of the magnetic gap. The insulating resin layer 43, however, is required to have a certain thickness, about 1.5 to 2.5 .mu.m, for example, because the shoulder of the magnetic pole 161 at the end of the upper magnetic core 16 rests on part of the insulating resin layer 43, defining the apex of the magnetic head.
Thin film conductors of the bottom-layer thin film coil 41 are arranged in parallel to each other on the insulating resin layer 43. Another insulating resin layer 44 is packed in such a manner as to embed the bottom-layer thin film coil 41. Thin film conductors of the upper-layer thin film coil 42 are formed in parallel to each other on the insulating resin layer 44, and still another insulating resin layer 45 is packed in such a manner as to embed the upper-layer thin film coil 42. An upper magnetic core 16 is formed on top of the insulating resin layer 45. A magnetic path for the thin film magnetic head is formed through the upper and lower magnetic cores 16 and 15.
The width of the thin film conductors of the thin film coils 41 and 42 is normally 2 to 4 .mu.m, and the intervals of the thin film conductors are of almost the same size. With the growing trend toward miniaturization of thin film magnetic heads, however, their sizes are expected to be gradually reduced; the width of the thin film conductors is expected to be reduced to 1.2 .mu.m, or even to 1 .mu.m in the future, and the intervals of the thin film conductors also are expected to be reduced to 1.2 .mu.m, or to 0.8 to 1 .mu.m in the future. The thickness of the thin film conductors, which is normally 2.5 to 4 .mu.m, is required to be at least about 2 .mu.m because too thin a thickness of the thin film conductors could increase the electrical resistance of the coil. Insulating layers of about the same thickness as the thin film conductors must be provided above and below the thin film conductors. Since the two or three-layer coil is provided between the lower and upper magnetic cores 15 and 16, the magnetic path formed is normally 20 .mu.m in height and 50 .mu.m in length, with the total magnetic path length being approximately 140 .mu.m. The inductance of the thin film magnetic head having such a magnetic path is about 0.1 to 0.12 .mu.H (frequency: 1 MHz) with a 11-turn coil.